public static CoursesCounter Incrementing(CoursesCounter existingCounter, CourseId courseId)
        {
            List <CourseId> coursesId = existingCounter.ExistingCourses;

            coursesId.Add(courseId);

            return(Create(existingCounter.Id, CoursesCounterTotalMother.Create(existingCounter.Total.Value + 1), coursesId));
        }